C-使用Malloc时的阀门错误

Question

我正在使用valgrind来修复我的C程序中的内存泄漏，并且有一个特定的功能似乎是大多数valgrind错误的来源

typedef struct Array {
    int capacity;
    int size;
    void **items;
} Array;
Array *createArray(int capacity) {
    Array *array = malloc(sizeof(Array));
    array->capacity = capacity;
    array->size = 0;
    void **items = malloc(sizeof(void *) * array->capacity *  sizeof *items);
    if(items == NULL) {
        exit(1);
    }
    array->items = items;
    return array;
}

createArray函数的第一行是在Valgrind中丢弃以下错误

1,296 (16 direct, 1,280 indirect) bytes in 1 blocks are definitely lost in loss record 34 of 42

我不是以正确的方式使用Malloc来分配内存？

Answer 1

如上所述，尚不清楚为什么您将items分配给：

 void **items = malloc(sizeof(void *) * array->capacity *  sizeof *items);

(本质上分配了8x(sizeof "a pointer"的其他倍数(指针数，而不是所需的指针(

相反，如果要为items分配array->capacity指针，请使用：

void **items = malloc(array->capacity * sizeof *items);

您的valgrind错误看起来不像是错误，但是在您分配的内存上不调用free的结果，而valgrind则报告丢失的字节(仍然可以在出口时到达(。您可以使用简单的destroyArray功能轻松释放出口的内存，类似于：

void destroyArray (Array *array) {
    for (int i = 0; i < array->size; i++)
        free (array->items[i]);
    free (array->items);
    free (array);
}

将其完全放置，您可以做类似：

的事情

#include <stdio.h>
#include <stdlib.h>
typedef struct Array {
    int capacity;
    int size;
    void **items;
} Array;
Array *createArray (int capacity) {
    Array *array = malloc (sizeof *array);
    array->capacity = capacity;
    array->size = 0;
    void **items = malloc(array->capacity *  sizeof *items);
    if(items == NULL) {
        exit(1);
    }
    array->items = items;
    return array;
}
void destroyArray (Array *array) {
    for (int i = 0; i < array->size; i++)
        free (array->items[i]);
    free (array->items);
    free (array);
}
int main (void) {
    Array *a = createArray (10);
    printf ("%d capacityn", a->capacity);
    destroyArray (a);
    return 0;
}

(注意：在尝试使用array之前，您还应该验证Array *array = malloc (sizeof *array);成功和(array != NULL)(

内存使用/错误检查

$ valgrind ./bin/allocstruct
==5777== Memcheck, a memory error detector
==5777== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==5777== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==5777== Command: ./bin/allocstruct
==5777==
10 capacity
==5777==
==5777== HEAP SUMMARY:
==5777==     in use at exit: 0 bytes in 0 blocks
==5777==   total heap usage: 2 allocs, 2 frees, 96 bytes allocated
==5777==
==5777== All heap blocks were freed -- no leaks are possible
==5777==
==5777== For counts of detected and suppressed errors, rerun with: -v
==5777== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

看事物，让我知道这是否是您所关心的。